Signal receiver and warning device



March 38, 3948. 5.5. col-IN 2,437,875

SIGNAL RECEIVER AND WARNING DEVICE Filed July 9, 1945 Q Z mm U a. & E o E a 5 w m Q INVENTOR.

SEYMOUR B. COHN BY ATTQRNEY Patented Mar. 16, 1948 SIGNAL RECEIVER AND WARNING DEVICE Seymour B. (John, Cambridge, Mass, assigncr to the United States of America, by the Secretary of War as represented Application July 9, 1945, Serial No. 694,068

3 Claims. I.

This invention relates generally to electrical circuits and more particularly to an alarm devicefor a, radio signalling system.

An object of this invention is to provide a device for generating an interrupted warning noise or other indication when a signal exceeding a predetermined magnitud is received in a receiver, or other radio device, and for indicating the rela tive strength of such signal by the rate of interruption of the indication.

The desired result is accomplished by employing a diode-triode rectifier-amplifier tube with a relaxation oscillator in the plate circuit of the amplifier. Under quiescent conditions, a large plate current flows in the amplifier reducing the voltage of its plate below the supply value and thus impressing a voltage across the relaxation oscillator which is of insuficient value to fire that tube. When a signal of sufiicient strength is received a portion thereof is rectified by the diode.

and is fed back to the amplifier grid to lower it below cut-off. This results in a decrease in the plate and an increase in the plate voltage to nearly supply voltage value. This voltage is of sufiicient value to trigger the relaxation oscillator and cause the desired alarm.

Other objects, features, and advantages will suggest themselves to those skilled in the art and will become apparent from the following description taken in connection with the accompanying draw ng which is a schematic circuit diagram of 9. p1 cred embodiment of the invention.

Referring to the drawing the circuits embodyng the present invention are capacity coupled, as t it, to the output of an amplifier I I inan otherwis conventional receiver. Amplified signals are impressed on the grid 42 of a diode-triode vacuum tube $3. This tube primarily acts as an amplifier and signals below a predetermined intensity will be reproduced in the loudspeaker in a. convenil However, a portion of the voltage the plate is rectified between the cathode l5 and the diode plate 55. This rectified Voltage is fed back to grid [2 through resistor ll. Resistor E8 provides'a ground return for grid l 2. Resistor it, between cathode l5 and ground and shunted by capacitor 29, provides a bias of proper value on cathode l5. Resistor 2! and capacitor 22 provide coupling from triode plate circuit to the diode and resistor 2i prevents the diode from overloading the triode. The plate load of the amplifier portion of tube l3 comprises resistor 23. Resistance coupled to the plate circuit of tube l3 by resistors 24 and 25 which determine the ratio of the ordinary signal to the warning noise, is neon lamp 2 26 shunted by capacitor 27. Capacitively coupled to the plate circuit of tube I3 by capacitor 28 is loudspeaker, or other indicating device, 29.

When no signal or a signal below a predetermined intensity is presenton grid l2, the negative bias voltage fed back to grid l2 through resistor 47 from diode plate It is not sufi'icient to lower grid 12 below cutofi. Under these circumstances tube It operates as a normal amplifier average current flows from plate M to cathode l5.

This causes a relatively high voltage drop acrossplate load 23 and consequently the voltage on; triode plate I 4 is lowered. Consequently, insufiicient voltage exists to charge capacitor 2! to sufficient 'value to fire neon tube 25. Q

When a. signal above a predetermined value is present on grid l2, the rectified negative voltage applied to grid l2 from diode plate It causes a reduction of plate current through triode l3 and the plate load 23. It follows that the voltage drop across plate load 23 is negligible, therefore, the voltage on triode plate l4 approximates B+, the value of the plate supply voltage. This increased voltage is applied through resistors 24 and 25 to neon tube 26 and capacitor 2?. When the value of this voltage rises above the ignition potential of neon tube 26, the tube breaks down and ca.- pacitor 21 discharges through it. The resultant current through the neon tube causes it to glow and to produce a series of clicks in loudspeaker 29 as well as the signal itself. Thus the circuit gives both visual and audible warning in addition to conventional reception. The presence of capacitor 27 and the value of its capacity controls the rapidity of the firing of tube 26 for a given applied potential.

The circuit constants may be chosen so that the value of voltage impressed on neon tube 26 by the weakest signal for which it is desired to give an alarm will cause that tube to oscillate at a very low rate. As the signal becomes stronger the voltage impressed on the neon tube becomes larger and the rate of oscillation of neon tube 26 will increase. Consequently, an indication of signal strength is obtained by noting the rate of fiickering of the neon light or by the rate of repetition of clicks in the loudspeaker.

The arrangement of the diode producing bias created by the rectified signal on the triode grid, together with the high amplification of the triode, provides a circuit relatively insensitive to supply voltage fluctuations.

One or more conventional band pass filter circuits, such as 38, 3i, and 32, may be included in the receiver at any suitable place prior to the cirand a high cuit herein described and selected by conventional switching means 33 in order to limit the operation of the present circuit to signals of predetermined frequencies. These band pass filters may be designed to be as narrow or as wide as desired.

While there has been here described What is at present considered to be the preferred embodiment of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.

What is claimed is:

1. In radio receiving circuits, a diode-triode vacuum tube, means for impressing a signal voltage on the grid of the triode portion of said tube, means associated with said triode portion to amplify said signal voltage, means for reproducing all received signals by a loudspeaker, other means including the diode portion of said tube for rectifying said amplified signal voltage and for feeding said amplified and rectified voltage back to said grid whereby the potential on the plate of the triode portion increases, a condenser, means for impressing said plate potential on said condenser, a discharge path for said condenser comprising a gas filled diode which is non-conducting for all potentials lower than that resulting on the plate of said triode for a received signal of predetermined minimum voltage and warning -means operated by the discharge ofsaid condenser.

2. In radio receiving circuits, a diode-triode vacuum tube, means for impressing a signal voltage on the grid of the triode portion of said tube, means associated with said triode portion to amplify said signal voltage, means including the diode portion of said tube for rectifying said amplified signal voltage and for feeding said amplified and rectified voltage back to said grid whereby the potential on the plate of the triode portion increases, a condenser, means for impressing said plate potential on said condenser, a discharge path for said condenser comprising a gas filled diode which is non-conducting for all potentials lower than that resulting on the plate of said triode for a received signal of predetermined minimum voltage and warning means operated by the discharge of said condenser.

3. In radio receiving circuits, a diode-triode vacuum tube, means for impressing a signal ,voltage on the grid of the triode portion of said tube, means associated with said triode portion to amplify said signal voltage, audio indicator means for reproducing all received signals, other means including the diode portion of said tube for rectifying said amplified signal voltage and for feeding said amplified and rectified voltage back to said grid whereby the potential on the plate of said'triode portion is increased proportionally to the amplitude of the received signal, and a normally non-operative relaxation oscillator, means to impress the varying plate potential on said oscillator, said oscillator being adapted to oscillate when a potential in excess of a predetermined value appears on said plate, said potential resulting from a received signal having an amplitude in excess of a predetermined value, said audio indicator means being responsive to said relaxation oscillator in its operative state.

SEYMOUR B. COHN.

REFERENCES CITED The following references are of record in the 

